This Is How A Volcano's Pyroclastic Flow Will Kill You

Volcanoes are notoriously deadly, but there’s no more frightening a way to meet your own personalized doom than via a pyroclastic flow. These fast-moving ferocious fires look more like summoned demons from a videogame than anything natural – but what exactly happens when one hits you?

KARO, NORTH SUMATRA, INDONESIA - JUNE 20: Mount Sinabung spews pyroclastic smoke, seen from Tiga Kicat village on June 20, 2015 in Karo District, North Sumatra, Indonesia. According to The National Disaster Mitigation Agency, more than 10,000 villagers have fled their homes since the authorities raised the alert status of Mount Sinabung erupting to the highest level. (Photo by Ulet Ifansasti/Getty Images)

Pyroclastic flows are the signature fireworks of the most explosive kinds of volcanic eruptions. These mixtures of ash, lava blebs and broiling gas are normally at temperatures between 200°C and 700°C (390-1300°F), but they can exceed temperatures of 1,000°C (1,832°F); they move at speeds of around 80 kilometers (50 miles) per hour, but have been observed travelling at 700 kilometers per hour (about 450 miles per hour).

They tend to rush down the slopes of stratovolcanoes, the mountainous types responsible for the most explosive eruptions. Sometimes, when the ratio of gas to ash is higher, they are referred to as “pyroclastic surges.” These currents are so sparse that have been known to actually go up hills and across water, not just downslope. In short, if you see one coming towards you, there’s no escape unless you have an extremely agile helicopter.

Assuming you’re on the ground, you’ll first encounter the intense heat riding at the front of the flow. If it’s a surge, despite it being cooler than a flow, you will still combust; your skin will rupture and becoming blackened by the severe heat of the gas before most of the ash even touches you microseconds later.

Even hiding inside a building won’t save you. When a surge passes by, the temperature of the air in the environment around it can sometimes be about 300°C (570°F), enough to destroy anything living within mere moments, and certainly high enough to severely damage the linings of your lungs if you breathe any of this heated gas in. If it does hit you, any fabric you have on will quickly burn away, and if you’re wearing any metal, it’ll sear itself into your skin for as long as it is still intact.

Human remains of the victims of the 79 BC's Vesuvio Volcan eruption are lightened at the Pompeii Archaeological Site on August 6, 2011 as part of the show ''The Moons of Pompeii.'' The new version of the show is held every weekend since May 7 until the end of October. AFP PHOTO/MARIO LAPORTA (Photo credit should read MARIO LAPORTA/AFP/Getty Images)

A flow isn’t much better, as you’ll be sautéed as soon as the flow front hits you. In both cases, your muscles will suddenly contract, and you’ll curl up into something resembling a pugilistic pose. The ash and gas will rush into your airways and, if you had time to live after the extreme heat shock, you’d quickly asphyxiate.

Some of the famous Vesuvian victims in Herculaneum were found with their skulls blown apart. It appears that the heat of the surge was so extreme that their brains boiled, releasing trapped gases so quickly that it blew apart their heads.

Either way, all that would be left of you would be a charred skeleton – if you’re lucky.

There are a variety of pyroclastic flow formation mechanisms.

The first forms when an ash column emerging from an eruption catastrophically falls back to Earth. Perhaps the gas content of the magma has dropped and the explosive, decompressive thrust at the volcano's vent runs out of power. Maybe the turbulent ash column mixes in too much cold air, or the lava in the column has cooled down too much. Either way, when the ash plume suddenly becomes denser than the surrounding air, it collapses and falls back onto itself, producing pyroclastic flows.

Another, far rarer type, we need to go back to Mount St Helens as it was back in May 1980. This volcano didn’t just erupt out of its vent at the summit; a huge internal pressure build up had nowhere to go but sideways, and the volcano obliterated itself by forcing its contents out of its side in a devastating lateral blast.

The sudden collapse of a growing, viscous, gas-filled lava dome, as well as the spilling or "boiling over" of material from an eruptive vent can also trigger pyroclastic flows, particularly when the ground is steep enough, allowing gravitational forces to essentially drag them out.

Human remains of the victims of the 79 BC's Vesuvio Volcan eruption are lightened at the Pompeii Archaeological Site on August 6, 2011 as part of the show ''The Moons of Pompeii.'' The new version of the show is held every weekend since May 7 until the end of October. AFP PHOTO/MARIO LAPORTA (Photo credit should read MARIO LAPORTA/AFP/Getty Images)

Plenty of hikers, journalists, volcanologists and indeed civilians have met their ends at the hands of a pyroclastic flow. They are indiscriminate killers, wiping out anything and anyone in their path – well, unless your name was Ludger Sylbaris.

Sylbaris was living on the French-Caribbean island of Martinique in 1902. Although accounts differ as to why, he was imprisoned for a serious offence in the city of St. Pierre on the night of May 7. He was thrown into solitary confinement; his cell was both windowless and underground. It was even reinforced with bombproof walls in order to make sure he couldn’t escape.

Then, at breakfast time the very next day, Martinique's Mt. Pelée erupted and blackened the sky with a terrifying, apocalyptic ash cloud. When this collapsed, pyroclastic flows formed and rushed down into the city, completely flattening it and killing all 40,000 people living there.

Everyone was turned into dust – everyone, of course, except for the man in the bombproof cell. Although he was badly burned, he survived, and was rescued from the rubble four days later. He was pardoned of his crimes, and joined Barnum & Bailey’s travelling circus, where he was known as the man who lived through Doomsday.

Updated to include additional information about formation mechanisms.

KARO, NORTH SUMATRA, INDONESIA - JUNE 19: Residents look to sky as Mount Sinabung spews pyroclastic smoke, seen from Simpang Empat village on June 19, 2015 in Karo District, North Sumatra, Indonesia. According to The National Disaster Mitigation Agency, more than 10,000 villagers have fled their homes since the authorities raised the alert status of Mount Sinabung erupting to the highest level. (Photo by Ulet Ifansasti/Getty Images)

Robin George Andrews is a doctor of experimental volcanology-turned-science journalist. He tends to write about the most extravagant of scientific tales, from eruptions and hurricanes to climate change and diamond-rich meteorites from destroyed alien worlds - but he's alway...